The disclosure concerns a device to dry a web-shaped recording medium in a printer in which said recording medium is printed with ink. The disclosure also concerns an associated operating method.
High-capacity printers that operate according to the inkjet principle print to a web-shaped recording medium via application of aqueous ink without the print heads being moved for printing. The web-shaped recording medium can thus be moved with relatively high transport speed (for example 1.5 m/s), such that the necessity exists to dry the damp print image via suitable devices. One possibility exists in the heating of the recording medium.
A thermal fixing device to fix toner images on a belt-shaped recording medium in an electrophotographic printing apparatus is known from U.S. Pat. No. 5,568,241 (WO 94/09410). The device includes a thermoprinting fixing station, upstream of which is situated a preheating station. This preheating station includes a convexly curved preheating saddle that is heated by means of heating rods and over whose sliding surface the recording medium is transported. The saddle-shaped sliding surface is formed in a curved shape. Due to the curvature and the necessary web tension, a force component results over the length of the preheating saddle, which force component presses the recording medium onto the sliding surface and thus establishes a good thermal contact. A negative pressure device is additionally provided that generates a negative pressure between the sliding surface and the recording medium, via which the recording medium is drawn onto the sliding surface of the heating saddle and the water vapor that is released by the preheating is drawn off.
Due to the curvature and the friction, the web tension of the recording medium increases over the length of the heating saddle. The contact pressure force therefore also changes over this length, and the thermal transfer between the recording medium and the surface of the heating saddle is not constant, which can lead to a non-uniform heating of the recording medium. Furthermore, it is also difficult to individually adjust the necessary thermal transfer for different paper types, ink types and print speeds. A compensation with the aid of heat controllers is technically complicated and difficult. Add to this slip-stick effects that arise due to non-uniform mechanical friction between the sliding surface of the preheating saddle and the recording medium. These disruptive slip-stick effects in particular occur upon turning on and off the transport of the recording medium.
DE-A-27 17 119 describes a drying device for a recording medium that is printed with the aid of an inkjet print head. After leaving the print zone, the recording medium is directed over a heated paper guide plate and dried. A heating film serves for heating.
DE-A-36 42 204 describes a drying device for a recording medium that has been printed with a printer operated according to the inkjet principle. Before the ejection of the ink by the print head, the recording medium is heated so that sufficient heat is still stored in the recording medium even after the ink inks said recording medium.
US 2010/0073450 A1 describes a device to dry a web-shaped recording medium in an inkjet printer in which the ink head is moved back and forth over a paper surface to be printed. For this, the web-shaped recording medium is borne on a cuboid, heatable body and is charged with negative pressure so that a segment of the heatable paper web is held stationary for printing, and the heat transferred from the heatable body to the paper dries the ink. After printing, the paper web is then transported further in order to print a next segment.
US 2010/0245451 A1 describes an inkjet printer in which multiple rows of print heads are arranged transverse to the transport direction of a sheet-shaped paper. Situated opposite the print heads is a heatable body on which the sheet of paper rests. The paper is drawn on with the aid of negative pressure, whereby the ink is dried on the one hand and the print heads are cooled by the drawn air on the other hand.